Late summer algae blooms may cause problems in farm ponds

Harmful algal blooms (HABs) in farm ponds can pose risk to people, pets and livestock. Learn to recognize HABs when using farm ponds for swimming and watering livestock.

Most ponds and lakes support planktonic algae – the tiny, single-celled plants that float in the water column and form the base of the food web. They occur naturally and can grow rapidly with increasing water temperatures, lots of sunlight and excess nutrients such as phosphorus and nitrogen, entering the pond from fields or from unlimited livestock access. A recent Michigan State University Extension article explains the importance of clean and safe water sources for livestock during hot summer months.

Green planktonic algae are true plants and are fed upon by fish and other aquatic animals. But blue-green algae are technically not algae. They are cyanobacteria that possess chlorophyll and photosynthesize like plants. When either kind of algae multiplies so rapidly that they can be seen with the naked eye it’s called an algal bloom. Most green algal blooms are harmless, but a bloom of cyanobacteria is referred to as a harmful algal bloom (HAB) and should be avoided. This is because, in high concentrations, cyanobacteria can produce toxins that can pose health risks to people, pets and livestock.

The toxic nature of cyanobacteria results in little or no control by fish and other animals as these animals usually avoid feeding on cyanobacteria. Because of this and other factors, blue-green algae often outcompete green algae for nutrients in the water column. They multiply rapidly (bloom) in both the shallow, quiet, sunny parts of the pond and in open water.

Algal Bloom

Photo: A harmful algal bloom (HAB) in a farm pond. Credit: Lois Wolfson

According to Michigan Sea Grant, “Blooms can range in color from red to bright, neon green to more blue-green. A bloom can look like a scum, foam or mat on top of the water or like paint that has been spilled in the water. They are also sometimes accompanied by an earthy, pungent or musty smell. However, not all algal blooms give off an odor or affect the appearance water and toxins can remain present in the water even when a bloom has dissipated.”

A bloom of cyanobacteria can produce neurotoxins, liver toxins and skin irritants in concentrations that may be harmful. People, pets and livestock that consume large amounts of toxins produced by HABs may experience an array of symptoms from muscle cramps, nausea and vomiting to paralysis, cardiac or respiratory difficulty, and even liver failure. Contact with skin irritants, found in nearly all blue-green algae blooms, can produce rashes and gastrointestinal distress.

In 2012, the University of Georgia Cooperative Extension observed several clinical symptoms, including extreme weight loss and bloody diarrhea, in cattle exposed to a HAB in a farm pond. Click here to find a video about their findings including a full list of clinical symptoms and excellent photos of harmful algal blooms.

HABs may persist for a day or two up to several weeks, depending on pond conditions. It is important that farmers using ponds to water livestock learn to recognize HABs and avoid contact. HABs are also a concern for Michigan inland lakes. Michigan Sea Grant recommends, “When in doubt, stay out.” To learn more about HABs and how to recognize them, visit the Michigan Sea Grant page: Harmful Algal Blooms in the Great Lakes.

Related Articles